The nitroglycerin (NTG) exercise test can help in detecting ischemia in the presence of right bundle branch block ( RBBB), left bundle branch block ( LBBB), or digitalis-induced exercise ST changes and in excluding ischemia when a falsely positive test is suspected. This treadmill test has 3-min stages at 10% grade starting at 1.5 mph and progressing in 0.5 mph increments until ST depression is observed. NTG is then given as exercise continues at the ischemia-provoking work load for up to 10 min. Among 3 patients with RBBB, 5 with LBBB, 1 on digitalis and 2 with presumed falsely positive tests, those whose ST depression lessened after NTG had ischemic thallium exercise scans; those with no change in ST depression after NTG had normal thallium images. Additional studies are needed to verify the consistency of these findings among a larger group of patients.